1. Field of the Invention
The present invention relates generally to the field of pressure atomizing liquid fueled burners and, more particularly, to a method and apparatus for increasing the turndown capability of oil pressure atomizing burners using aeration throttling.
2. Description of the Prior Art
Oil pressure atomizing burners, also known as mechanical pressure atomizing burners, operate on the principle that when oil under pressure is permitted to expand through a small orifice it tends to break into a spray of very fine droplets which are suitable for combustion. These burners are usually designed to operate with oil pressures as high as 75 to 100 psi and viscosities of from less than 50 to 100 SSU. The principle upon which these burners operate requires that the pressure drop across the atomizing orifice be maintained high and as nearly constant as possible in order to achieve the necessary spray of fine atomized droplets. Because it is not possible to maintain the required pressure drop at lower flows, turndown, which is defined as the ratio of maximum to minimum input rates, in the operation of such burners has traditionally been very severely limited or has not been used at all and the burners have been operated in an on-off mode only. This, of course, results in inferior temperature control and lower furnace efficiency.
It has been found that improved atomization, i.e. smaller droplet size also permits better mixing of the air and the fuel and reduces the tendency to form soot. Atomization can be improved by increasing the internal energy of the fuel as by preheating the fuel. One such study and analysis which demonstrates the benefits of maximizing the internal energy of the fuel per unit volume and minimizing the apparent viscosity for atomization prior to combustion is found in Study of a Thermal Aerosol Oil Burner, by J. E. Janssen, J. J. Glatzel, E. R. Wabasha and V. Bonne, published in EPA Report 600/7-77-108, September, 1977.
Inasmuch as the cost of oil and other liquid fuels has increased greatly in the last few years, concern with more efficient fuel utilization in oil burners has also become much greater. Thus, there has existed a need to have a great deal more control over the fuel consumption of a burner while maintaining the best combustion efficiency possible for that burner at all possible flows. Thus, there has existed a need for accomplishing more effective burner turndown while maintaining an even increasing combustion efficiency in pressure atomizing liquid fuel burners.